The present invention relates to a collimator and a radiation irradiator. Particularly, the invention is concerned with a collimator for a radiation, e.g., X-ray, and a radiation irradiator provided with the collimator.
In a radiation irradiator there is used a collimator for controlling the irradiation range of a radiation. The collimator has an aperture which permits a radiation to pass therethrough, and the radiation cannot pass through other than the aperture. Thus, the irradiation range of the radiation is controlled by the aperture. The degree of opening of the aperture can be changed to adjust the irradiation range of the radiation.
As shown in FIG. 10, the aperture-adjustable collimator has a pair of movable plate members having a radiation shielding property, i.e., blades 901 and 901′. The blades 901 and 901′ are disposed so that respective end faces are opposed to each other, and are movable in directions opposite to each other in a plane parallel to their surfaces. For widening the aperture, the pair of blades 901 and 901′ are moved away from each other, while for narrowing the aperture, the both blades are moved to close to each other. Thus, the aperture becomes maximum when the pair of blades are remotest from each other, and becomes minimum when both blades are closest to each other.
In a collimator having a large aperture adjusting range, there are used blades of a large area. If the blade area is large, an external form of the collimator comes to have a large size corresponding to a maximum moving distance of blade outer edges, as shown in FIG. 11.
In a mammography apparatus which makes fluoroscopy of the breast with X-ray, a collimator assumes a position confronting the face of a subject and so it is preferable that its external form be as small as possible. However, in the case of a mammography apparatus capable of making tomography, an increase in external form of the collimator has heretofore been unavoidable because a large aperture is needed.